Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, 21205, USA.
Medtronic Inc., Littleton, MA, 01460, USA.
Med Phys. 2018 Nov;45(11):4857-4868. doi: 10.1002/mp.13167. Epub 2018 Oct 9.
To assess the imaging performance and radiation dose characteristics of the O-arm CBCT imaging system (Medtronic Inc., Littleton MA) and demonstrate the potential for improved image quality and reduced dose via model-based image reconstruction (MBIR).
Two main studies were performed to investigate previously unreported characteristics of the O-arm system. First is an investigation of dose and 3D image quality achieved with filtered back-projection (FBP) - including enhancements in geometric calibration, handling of lateral truncation and detector saturation, and incorporation of an isotropic apodization filter. Second is implementation of an MBIR algorithm based on Huber-penalized likelihood estimation (PLH) and investigation of image quality improvement at reduced dose. Each study involved measurements in quantitative phantoms as a basis for analysis of contrast-to-noise ratio and spatial resolution as well as imaging of a human cadaver to test the findings under realistic imaging conditions.
View-dependent calibration of system geometry improved the accuracy of reconstruction as quantified by the full-width at half maximum of the point-spread function - from 0.80 to 0.65 mm - and yielded subtle but perceptible improvement in high-contrast detail of bone (e.g., temporal bone). Standard technique protocols for the head and body imparted absorbed dose of 16 and 18 mGy, respectively. For low-to-medium contrast (<100 HU) imaging at fixed spatial resolution (1.3 mm edge-spread function) and fixed dose (6.7 mGy), PLH improved CNR over FBP by +48% in the head and +35% in the body. Evaluation at different dose levels demonstrated 30% increase in CNR at 62% of the dose in the head and 90% increase in CNR at 50% dose in the body.
A variety of improvements in FBP implementation (geometric calibration, truncation and saturation effects, and isotropic apodization) offer the potential for improved image quality and reduced radiation dose on the O-arm system. Further gains are possible with MBIR, including improved soft-tissue visualization, low-dose imaging protocols, and extension to methods that naturally incorporate prior information of patient anatomy and/or surgical instrumentation.
评估 O 臂 CBCT 成像系统（美敦力公司，马萨诸塞州利特尔顿）的成像性能和辐射剂量特性，并通过基于模型的图像重建（MBIR）证明改善图像质量和降低剂量的潜力。
进行了两项主要研究，以调查 O 臂系统以前未报道的特性。第一项是使用滤波反投影（FBP）研究剂量和 3D 图像质量，包括改进几何校准、处理横向截断和探测器饱和以及采用各向同性的余弦窗函数。第二项是实现基于 Huber 惩罚似然估计（PLH）的 MBIR 算法，并研究降低剂量时的图像质量改善。每项研究都涉及在定量体模中的测量，作为分析对比度噪声比和空间分辨率的基础，以及对人体尸体进行成像，以在实际成像条件下检验结果。
系统几何结构的视相关校准提高了重建的准确性，重建的半峰全宽从 0.80 毫米降低至 0.65 毫米，并且对骨（例如颞骨）的高对比度细节产生了微妙但可察觉的改善。头部和身体的标准技术方案分别施加 16 和 18 毫戈瑞的吸收剂量。对于低到中等对比度（<100HU）的固定空间分辨率（1.3 毫米边缘扩展函数）和固定剂量（6.7 毫戈瑞）成像，PLH 在头部提高了 FBP 的 CNR 48%，在身体提高了 35%。在不同剂量水平的评估表明，头部剂量降低 62%时 CNR 增加 30%，身体剂量降低 50%时 CNR 增加 90%。
FBP 实施（几何校准、截断和饱和效应以及各向同性余弦窗函数）的多种改进提供了在 O 臂系统上改善图像质量和降低辐射剂量的潜力。MBIR 进一步提高了软组织可视化、低剂量成像方案的性能，并扩展到自然地整合患者解剖结构和/或手术器械先验信息的方法。
